Hello Kate
As no-one else has come up with a definitive answer, the following may be helpful:
You don't say what is sticking - on my control, the tiny brass button [it might have had a rubber cover once upon a time] that you press in to disengage the gears from the throttle needs a regular squirt with an aerosol thread Penetrating or Releasing fluid otherwise it sticks in the "In" or "Gears disengaged" position, whereupon it needs another squirt followed by a blow with a blunt instrument to dislodge it....
If not that, then if your control works freely when your gears are disengaged, suspect your gear cable & linkage, and if your control is always stiff, start with the throttle cable & its linkage. If either of the "push/pull" cables have been visibly kinked or restricted into too tight a radius by "stuff" in your cockpit locker - a not uncommon occurrence - then the affected cable will need to be replaced if kinked, or allowed to take up a larger radius curve. If you have to replace cable[s], brand/manufacturer is not usually critical but the end fittings often are.
If the cables look fine, then before spending any money, have a look inside the control box and wash off all the age hardened grease and dirt with white spirit or a degreasing agent like aerosol Gunk, and regrease lightly with a water resistant grease like Ramonal, or even just plain old Vaseline. Do the same with the linkages at the engine and gearbox ends of the cables. You may surprise yourself with how smoothly your controls now work!
If you do have to renew the cables, or the box [unlikely unless something has actually broken inside it] then the description of your box sounds just like the one on my 1989 P27 with Yanmar engine - there's a high probability that the control box was supplied with the engine, and hence in my case is a Yanmar branded control...so if you want to try to match the existing exactly, then I'd start by talking to the Dealer for your engine manufacturer.
But few marine engine manufacturers make their own controls - they buy them in re-branded from a specialist control manufacturer like Teleflex/Morse [USA] or Ultra-Flex [Italy]. Given the vintage, chances are Seal/Parker Yanmar controls were made by Teleflex...and Teleflex cables are a pretty universal fit...and just as with cars, the component manufacturer's prices [ie Teleflex] will be usually be much lower than the engine manufacturer's spare parts.
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sincerely
Geoff Sheddick
Parker 27/146 "Stroller'
Geoff Sheddick
Parker 27/146 "Stroller'